Device for creating electrostatic charge or discharge

ABSTRACT

A device for electrostatically charging or discharging surfaces of a web or sheet material or charging photoconductive insulating layers comprising two mounted rows of needles which are separated from one another but parallel to one another with each row being of a different electrical potential. Within each row the distance between adjacent needles remains constant. Furthermore each needle of one row is coordinated at an acute angle with a needle of the other row by separating walls extending from one row of needles to the other row of needles. The angle between coordinated needles is below 45*. The needle distance is about three needle thicknesses with the needle thickness ranging between about 0.1 to 1 mm. Preferably the device includes a counterelectrode having an electrical potential equal to one row of needles.

United States Patent [1 1 Marx 1 1 DEVICE FOR CREATING ELECTROSTATIC CHARGE OR DISCHARGE [75] Inventor: Gerhard Marx, Hahn, Germany [73] Assignee: Kalle Aktiengesellschaft,

Wiesbaden-Biebrich, Germany [22] Filed: Sept. 14, I972 [21] Appl. No.: 289,053

[30] Foreign Application Priority Data Sept. 17, 1971 Germany P 21 46 539.4

[52] US. Cl. 317/2 F, 317/4, 317/262 A [51] Int. Cl. HOlt 19/04 [58] Field of Search 317/2 F, 4, 262 A [56] References Cited UNITED STATES PATENTS 3,335,322 8/1967 Epstein ct a1. 317/4 3,483,374 12/1969 Erben 317/4 FOREIGN PATENTS OR APPLICATIONS 228,800 7/1969 U.S .S.R. 317/2 F 1111 3,792,312 [451 Feb. 12,1974

Primary Examiner-L. T. Hix Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A device for electrostatically charging or discharging surfaces of a web or sheet material or charging photoconductive insulating layers comprising two mounted rows of needles'which are separated from one another but parallel to one another with each row being of a different electrical potential. Within each row the distance between adjacent needles remains constant. Furthermore each needle of one row is coordinated at an acute angle with a needle of the other row by separating walls extending from one row of needles to the I other row of needles. The angle between coordinated needles is below 45. The needle distance is about three needle thicknesses with the needle thickness ranging between about 0.1 to 1 mm. Preferably the device includes a counterelectrode having an electrical potential equal to one row of needles.

5 Claims, 2 Drawing Figures DEVICE FOR CREATING ELECTROSTATIC CHARGE OR DISCHARGE This invention relates to a device for creating an electrostatic charge or discharge of surfaces of web or sheet material, particularly to creating an electrostatic charge of photoconductive insulating layers, consisting of rows of needles arranged transversely to the direction of travel of the material, in which all needle points are positioned the same distance from the surface of the material.

For eliminating an electrostatic charge from a material, it is known to use an arrangement consisting of a metal plate provided with bores or slits oblique to the direction of travel of the material, in the middle of which there are one or more point electrodes. A homo geneous charge which is necessary particularly for electrophotographic purposes is not achieved by this arrangement. Due to the fact that the needle is arranged in themiddle of a bore or in the middle of a longitudinal slit, electrons could issue to all sides but, according to experience, the needle is burned off in dependence on the direction first taken so that the flow of electrons always is forced in the same direction. In the case of an unfavorable burning-off, untreated narrow or wider zones result therefrom.

A charging device for xerographic copying also is known which has needle points arranged in series and obliquely to the direction of travel of the material to be treated with grounded U-shaped shielding rods arranged parallel to the needle points. This arrangement additionally has a potential in the form of a row of wires parallel to the treatment plane and to the straight lines of the needle points. Such an arrangement is not only complicated but also does not offer a homogeneous charge, particularly over a relatively long period of time of operation since the surfaces of the wires or of the U-shaped shielding rods after burning-off have a fixed emission direction so that formation of stripes occurs.

Another arrangement is known in which the needle points in several parallel rows with the same electric potential are arranged obliquely to the direction of travel of the material. This arrangement is disadvantageous in that a relatively large needle distance is necessary and the operation is possible only with the conveyance of the material being in a plane. This arrangement is also known in an embodiment which, in addition to needles of a lower voltage, has obliquely staggered needles of a higher voltage. This arrangement is complicated considerably thereby and, although a higher homogeneity can be achieved, the charge potential is at the same time considerably limited.

The object of the invention is to provide an electrostatic charge or discharge device which overcomes the described drawbacks and guarantees a'charge ordischarge satisfying the highest demands at an operating speed as high as possible and over a relatively long period of operation time.

The present invention provides a device which is characterized in that it consists of two needle rows separated from one another and parallel to one another and of different electric potential and with a constant needle distance. Each needle of the one, row of needles is coordinated at an acute angle to a needle of the other row of needles by intermediate separating walls. The

device preferably also has a counter-electrode with the electrical potential of a row of needles.

The invention by the arrangement of only two rows of needles provides a relatively narrow apparatus suitable for treatment of the material in a plane as well as in a curved path. Separation of the streams of electrons from one another by the separating walls furthermore permits a very dense arrangement of the needles which due to the constant distance from one another is conductive to a homogeneous charge or discharge. Furthermore, the undesirable influence related to the direction of the stream of electrons of the needle points due to burning-off is now taken advantage of in the present invention by the stream of electrons being forced in one direction right from the beginning. This is achieved by the intermediate separating walls the height of which is such that sparking-over does not take place.

The acute-angle arrangement furthermore permits repeated moving across each portion of the material to be treated so that, even in the event of the failure of a pair of needles, homogeneous charging or discharging takes place by the neighboring electron streams.

An arrangement has provided suitable in which the separating walls are so oblique to the direction of material movement that each portion of the material moving in the treatment plane E (FIG. 1) is guaranteed treatment three times. Therefore, in a preferred embodiment, the acute-angle is below 45 which guarantees repeated treatment of any portion of the material in a relatively narrow apparatus.

The device of the invention permits a long operational time without trouble at an optional high-voltage in the relatively low or high range.

Examples of materials the surfaces of which can be charged or discharged are paper, textiles, leather, rubber, metal foils coated with plastics material, and corresponding composite materials. The device of the invention is preferably used for the electrostatic charging of photoconductive insulating layers. The device of the invention is particularly suitable for charging photoconductive insulating layers in reenlargement apparatus because of its intense and uniform effect.

With known procedures, such a homogeneous charge could not be achieved. It has been found that the stream issues better from points than from very flat bodies, the points having been selected carefully for suitability with respect to configuration and grinding.

The invention is more fully described by way of the attached drawings, of which FIG. 1 is a perspective view of the device of the invention with a counter electrode and FIG. 2 is an enlarged plan view.

With reference to FIG. 1 body 1 has a length equal I to the width of known insulating material, such as ceramics or plastics material, and grooves 8 (FIG. 2) incorporated in one of its surfaces. At each end of the grooves bores or apertures for the insertion of needles 4 are provided.

The depth of the groove depends on the high-voltage to be applied and must be such as to prevent sparkingover. It thus depends on the needle distance B and on the height of the protruding needle point 5. The needle distance is generally constant but may vary, depending on the purpose of use. In the preferred case, a needle distance of about three needle thicknesses has proved suitable. The thickness of the separating wall 7 also is determined thereby, which may be one needle thickness or more.

The bores of the opposing needle rows may be arranged optionally. They may be obliquely staggered or so staggered that a bore is on the mid-vertical on the distance between two opposing bores. Because of the favorable mechnical stability of the insulating body, the latter arrangement is of advantage.

The needles 4 are made of an electroconductive material, such as steel, a special steel or other metal alloy or noble metal. The needles are arranged in two rows, 2, 3, which are each conductively connected with one of the metal profiles arranged parallel to one another and protrude from the base of the grooves. it has proved advantageous to have only the ground point protrude. The needle thicknesses are in the range of from about 2 mm to about 0.1 mm. Depending on the material 6 to be treated, thicker or even thinner needles may be used. For the discharge of textile surfaces thicker needles are used. For the electrostatic charging of photoconductive insulating layers extremely thin needles with thicknesses between about 0.1 and about 1 mm with markedly fine points are employed.

The points 5 of the needles 4 forming a plane among themselves which is parallel or substantially parallel to the material surface have a distance from the material in the range from about 5 to 30 mm in dependence on the high-voltage applied.

The material 6 to be treated is conveyed in the direction C transversely to the longitudinal edge of the insulating body 1. The oblique arrangement of the coordinated needles 4 guarantees that, even in the case of an unavoidable failure of a pair of needles, each portion of the surface of the material is treated in that the treatment may be carried-out by neighboring pairs of needles.

The feed speed of the material to be treated is optional and may vary between about 1 and 50 m/min. Speeds between about 4 and 20 m/min. are particularly suitable. The device of the invention permits the application of highvoltage ranging between about 1 and kv. v

Particularly for charging electrophotographic materials, a counter electrode 9 wi th the same potential as that of a row of needles is necessary, which may be in the form of a roller or another transporting means.

In an embodiment for the electrostatic charging of electrophotographic insulating layers of the size DIN A2, the device of the invention has the following mea surements: The insulating body I has the dimensions 440 X 30 X 10 mm. the groove depth is 12 mm, the needle thickness is 1 mm, the distance between needles is 3 mm, the groove width is 1 mm, the width of the separating'wall 7 is 1 mm, the distance (A) of two coordinated needles 4 is 10 mm, and the angle of the groove to the longitudinal edge of the insulating body is about 42.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A device for electrostatically charging or discharging of surfaces of material, comprising two rows of needles arranged transversely to the direction of travel of the material, with the points of said needles forming an area parallel to the surface of the material, said rows being separated from one another, parallel to one another and of different electric potential, with each row having a constant distance between needles therein,

4. The device of claim 1 wherein the longitudinally inserted needles are so arranged that a needle is on the mid-vertical on the distance between two opposing needles.

5. The device of claim 1 wherein the needle thicknesses range between about 0.1 and about 1 mm. 

1. A device for electrostatically charging or discharging of surfaces of material, comprising two rows of needles arranged transversely to the direction of travel of the material, with the points of said needles forming an area parallel to the surface of the material, said rows being separated from one another, parallel to one another and of different electric potential, with each row having a constant distance between needles therein, and with each needle of one row of needles being coordinated at an acute angle to a needle of the other row of needles by intermediate separating walls.
 2. The device of claim 1 wherein the acute angle is below 45*.
 3. The device of claim 1 wherein the needle distance of a row of needles is about three needle thicknesses.
 4. The device of claim 1 wherein the longitudinally inserted needles are so arranged that a needlE is on the mid-vertical on the distance between two opposing needles.
 5. The device of claim 1 wherein the needle thicknesses range between about 0.1 and about 1 mm. 